Conductive materials are used in a wide variety of applications including, for example, EMI shielding (including cables, structures, and enclosures), antennas, conductive wires and other conductive surfaces, current collectors, black body absorbers, thermal conductors, and the like. Due to their high conductivity values, metals are most often used for these purposes. However, the significant densities of most metals can sometimes result in structures that are too heavy for efficient use in certain situations, such as aerospace and aeronautic applications.
Carbon nanotubes (CNTs) have been proposed for use in a number of applications that can take advantage of their unique combination of chemical, mechanical, electrical, and thermal properties. Various difficulties have been widely recognized in many applications when working with individual carbon nanotubes. These difficulties can include the propensity for individual carbon nanotubes to group into bundles or ropes, as known in the art. Although there are various techniques available for de-bundling carbon nanotubes into well-separated, individual members, many of these techniques can detrimentally impact the desirable property enhancements that pristine carbon nanotubes are able to provide. In addition to the foregoing, widespread concerns have been raised regarding the environmental health and safety profile of individual carbon nanotubes due to their small size. Furthermore, the cost of producing individual carbon nanotubes may be prohibitive for the commercial viability of these entities in many instances.
Carbon nanotubes have been proposed as a replacement for metals in some applications due to their significant electrical conductivity and much lower weight. One illustrative use for carbon nanotubes that has been proposed in this regard involves electromagnetic radiation shielding applications, particularly shielding against microwave energy. However, manipulating carbon nanotubes into a conductive layer that can be suitable for shielding applications has proven challenging. Foremost, the significant propensity for individual carbon nanotubes to agglomerate with one another in ropes or bundles can make it problematic to reproducibly incorporate carbon nanotubes in a composite material or to coat a substrate with carbon nanotubes in a conductive layer having sufficient optical coverage to affect shielding of electromagnetic radiation. As used herein, the term “optical coverage” refers to the extent to which a material blocks the leakage of electromagnetic radiation therethrough. Moreover, for coating applications, the small size of individual carbon nanotubes can make it problematic to directly apply the carbon nanotubes to porous substrates due to their propensity to pass through the pores defined therein, rather than residing on the substrate surface as a coating. Similar difficulties can be encountered with other conductive nanomaterials such as nanoparticles and graphene, for example.
In view of the foregoing, production of carbon nanotubes in a form that renders them more amenable for coating applications would be highly desirable, particularly for purposes of conveying electromagnetic radiation shielding. The present disclosure satisfies the foregoing needs and provides related advantages as well.